World of Tanks is still drawing me in on a daily basis. I don't play it for very long, typically 30 minutes or so, but the design of the game is such that that works out just fine. I do sometimes have a little difficulty dragging myself away (just one more match!) but for the most part it's great bite-sized gaming. The fact that I've always had a certain fondness for WWII tanks and aircraft hasn't hurt either. I'd love to see them expand the scope of the game, but that's another post.
One of the aspects of WoT that keeps it engaging is how varied the experience is on a daily basis. I suppose it's no different than any game with PvP, but the variance seems much higher than, for example, warfronts in Rift. Luck of the draw plays a big part, in that the enemies vehicle types arrayed against you have a huge impact on the outcome of the match. The skill of your opponents has a big impact, as does how aggressively the two teams play. Finally, the tier distribution has a huge impact as well.
I've had battles where I was top of the list (T1 heavy tank) with no heavies on the enemy team, no artillery, and only one or two tank destroyers, and pretty much mopped the place up. I've had battles where I was top of the list (T1 heavy tank) with no heavies on the enemy team, but lots of artillery and tank destroyers and been pinned down within the first 2 minutes of the battle and gutted by concentrated fire. I've had battles where I was middle of the list yet ended the match still alive with 3 kills and the rest of my team wiped out and our base captured. I've had battles where my M5 Stuart (light tank) raced up a road just to get one-shotted by a hidden enemy tank destroyer in the first 30 seconds of a match. I've had battles where my M2 Medium tank rolled around the map popping enemy artillery like grapes (gotta love a 75mm howitzer on a tier 3 tank).
World of Tanks seems to be a roller coaster of highs and lows. Some battles are really great, some are really terrible. I hardly ever see anything in the middle, so much so that finishing a battle alive but with no kills is almost exciting. Despite the fact that WoT's content is really very limited, the highs keep me coming back for one more match, and the lows keep it from getting monotonous. Although I find the unbalanced design of the matchmaking system frustrating at times, I have to admit it keeps the game interesting.
Now if they could just add some sort of persistent campaign with sides divided up by nationality . . .